1. Field of the Invention
The present invention relates to a gear mechanism having a pinion and a rack, a large diameter gear meshing therewith and a webbing retractor for use in a seat belt system of a vehicle for taking out and taking up a webbing.
2. Description of the Related Art
Some types of the webbing retractor for use in the seat belt system contain a mechanism (pretensioner) for cancelling a slack of the webbing by taking up the webbing to tension it at the time of an emergent deceleration like a collision of the vehicle. Webbing retractors apparatus having such a pretensioner have been disclosed in for example, Japanese Utility Model Application Publication (JP-Y) No. 55-21696 and Japanese Patent No. 2500192.
The webbing retractor described in Japanese Utility Model Application Publication (JP-Y) No. 55-21696 comprises a drum to which an end portion of a seat belt (webbing) is fixed, a pinion fixed to a rotation shaft of this drum coaxially therewith, a piston supported slidably in a cylinder and a rack connected to a piston rod of this piston. Before the piston is actuated, the rack is held at a position in which it does not mesh with the pinion. Upon an emergency like a collision of a vehicle, gas is supplied into the cylinder by a gas generator and the piston is moved in a predetermined direction by this gas pressure. At the same time, the rack meshes with the pinion so as to rotate the pinion in a direction for taking up the seat belt. Therefore, according to the seat belt retractor described in Japanese Utility Model Application Publication (JP-Y) No. 55-21696, because the rack is held at a position in which it is not in mesh with the pinion before the piston is actuated, the pinion and the drum are capable of rotating without being interfered by the rack. Further, because the rack meshes with the pinion upon an emergency so as to rotate the pinion in the direction for drawing in the seat belt, the seat belt is wound up by the drum fixed to the pinion to cancel a slack of the seat belt.
The webbing retractor disclosed in Japanese Patent No. 2500192 comprises a belt drum for winding up a belt web (webbing), a pinion linked with this belt drum through a flywheel linking device and gear transmission means for transmitting only a rotation of a single direction, a rack meshing with this pinion and a piston cylinder driving unit in which a piston thereof is connected to the rack. Upon a collision of a vehicle, the piston cylinder driving unit is actuated by gas generated by a gas generator so as to move the rack. As a result, the pinion is rotated in the direction for taking up the belt web and the gear transmission means increases an angular velocity of the pinion and transmits the rotation of the pinion to the belt drum. Therefore, according to the belt retractor disclosed in Japanese Patent No. 2500192, because the gear transmission means increases the angular velocity of the pinion and transmits the rotation of the pinion to the belt drum, a taking-up amount for the belt web by the belt drum relative to a traveling amount of the rack can be made large.
However, in the webbing retractor described in Japanese Utility Model Application Publication (JP-Y) No. 55-21696, because upon an emergency, after the rack is moved from a position in which it is not in mesh with the pinion to a position in which it comes in mesh with the pinion, it rotates the pinion, when the rack meshes with the pinion, a large impact load is applied to the teeth of the pinion as an initial driving force. Therefore, in the webbing retrator having such a structure, the strength of the pinion teeth needs to be very high and therefore, it is difficult to reduce the size of the pinion. As a result, to secure a taking-up amount of the webbing necessary for an emergency time, the length of the rack and traveling range thereof need to be large, so that the retractor must be large-sized.
In the webbing retractor described in Japanese Patent No. 2500192, because the gear transmission means increases the angular velocity of the pinion, the traveling range of the rack can be reduced without reducing the number of the teeth of the pinion. However, since in the webbing retractor having such a structure, its gear transmission means is structured with at least two gears, the number of parts increases thereby leading to increases in production costs and weight.
Accordingly, the present invention has been achieved in views of the above described problems and therefore, an object of the invention is to provide a gear mechanism in which, even if a large initial driving force is applied from a gear to a pinion, teeth of the pinion are prevented from being damaged and a small-sized webbing retractor having the same gear mechanism.
According to a first aspect of the present invention, there is provided a gear mechanism comprising: a pinion; a gear meshing with said pinion; and an initial driving member provided on the pinion for receiving an initial driving force from the gear to rotate the pinion.
According to the gear mechanism having the above structure, at the same time when the gear in a stop state starts to drive the initial driving member, the initial driving member receives an initial driving force from the gear so as to rotate the pinion. As a result, the initial driving force is not applied from the gear directly to the teeth of the pinion or the initial driving force is applied indirectly to the teeth of the pinion. Thus, even when the initial driving force from the gear is large, the teeth of the pinion can be prevented from being damaged by the initial driving force.
The gear mentioned here refers to a gear having a larger diameter than the pinion, including a rack and a sector gear. In some case, the initial driving force is applied to the initial driving member in a condition that this gear is in mesh with the pinion, and in some case, the initial driving force is applied to the initial driving member from a position far from the pinion. The initial driving force mentioned here refers to a force which the gear applies to the pinion until the pinion is rotated by a predetermined rotation amount after the rotation of the pinion is started by the gear, and this initial driving force includes an impact force from the gear.
According to a second aspect of the present invention, there is provided a gear mechanism according to the first aspect, wherein the initial driving member is provided on the pinion coaxially therewith.
In the above described gear mechanism, the initial driving member can be supported by a shaft common to the pinion. Thus, any supporting shaft or bearing for supporting the initial driving member does not need to be added, thereby suppressing an increase of the number of parts.
According to a third aspect. of the present invention, there is provided a gear mechanism according to the first aspect, wherein the initial driving member supports a pressure receiving portion for receiving the initial driving force outwardly in a radius direction relative to the pinion.
In the gear mechanism having such a structure, in case where the direction of the initial driving force to be applied to the pressure receiving portion of the initial driving member by the gear is substantially parallel to a tangent line (pitch line) of a pitch circle on the pinion, the driving torque and angular velocity of the pinion can be changed by changing a distance from the pinion axis to the pressure receiving portion. Therefore, the driving torque and angular velocity of the pinion can be adjusted depending on the characteristic of the rotation load to be applied to the pinion at the initial phase of drive start.
According to a fourth aspect of the present invention, there is provided a gear mechanism according to the second and third aspects, wherein the gear or its supporting portion includes a recess for avoiding an interference with the initial driving member which rotates the pinion by receiving the initial driving force.
In the gear mechanism having the above described structure, the initial driving member which rotates the pinion by receiving the initial driving force is prevented from interfering with the gear or the supporting portion. Therefore, the pinion can be rotated continuously by the gear without releasing the initial driving member which rotates the pinion, from the pinion.
The gear supporting portion mentioned here refers to a member for supporting the gear movably in the driving direction and a member for transmitting a driving force to the gear, and includes, for example, a piston rod supporting a rack, gear rotation shaft and the like.
According to a fifth embodiment of the present invention, there is provided a gear mechanism according to the second and third aspects, wherein the initial driving member is fitted between teeth of the pinion detachably.
In the gear mechanism having the above described structure, since the initial driving member is fitted between the teeth of the pinion detachably, the initially driving member is capable of transmitting a torque securely to the pinion. Further, when the initial driving member receiving the initial driving force is released from the pinion, the initially driving member never interferes with the gear meshing with the pinion. Therefore, the pinion can be rotated continuously by the gear.
According to a sixth aspect of the present invention, there is provided a gear mechanism according to the fifth aspect further comprising a guide portion for allowing the initial driving member to rotate integrally with the pinion when the initial driving member engages the pinion to transmit the initial driving force to the pinion and for limiting a moving direction of the initial driving member for the initial driving member to be released from the pinion after the transmission of the initial driving force is completed.
In the gear mechanism having the above described structure, the guide portion for limiting the moving direction of the initial driving member makes the initial driving member to rotate integrally with the pinion when the initial driving force is transmitted to the pinion, and after the transmission of the initial driving force is completed, release the initial driving member from the pinion. As a result, the initial driving member can be prevented from falling out of the pinion during the transmission of the initial driving force. Thus, the initial driving force can be transmitted securely to the pinion through the initial driving member. Further, because the initial driving member does not interfere with the pinion and the gear after the transmission of the initial driving force is completed, the rotation of the pinion can be continued without being obstructed by the initial driving member.
According to a seventh aspect of the present invention, there is provided a gear mechanism according to the first aspect, wherein the initial driving member is supported swingingly around an axis different from that of the pinion while being fitted between teeth of the pinion detachably.
In the gear mechanism having the above described structure, because the initial driving member is fitted between the teeth of the pinion detachably, the initial driving member is capable of transmitting a torque to the pinion securely. After the initial driving member which has received the initial driving force is released from the pinion, the pinion can be rotated continuously by the gear because the initial driving member never interferes with the gear meshing with the pinion. Further, because the initial driving member is supported swingingly around a shaft disposed at a position different from the rotation shaft of the pinion, the initial driving member which has been released from the pinion can be held at a position in which it does not interfere with the pinion and the gear.
According to an eighth aspect of the present invention, there is provided a gear mechanism according to the secondseventh aspects, wherein a pressure receiving portion for receiving the initial driving force of the initial driving member is formed in an involute curve.
In the gear mechanism having the above described structure, as the pressure receiving portion of the initial driving member is formed in an involute curve, the torque and angular velocity of the pinion rotated by the initial driving member receiving the initial driving force can be substantially the same as the torque and angular velocity of the pinion rotating in mesh with the gear. Thus, the characteristics on the torque and angular velocity from a driving start of the gear mechanism to an end thereof can be made constant.
According to a ninth aspect of the present invention, there is provided a gear mechanism according to the first aspect, wherein the initial driving member is provided on the pinion so as to rotate integrally with the pinion while having an engagement portion outside a pitch circle of the pinion and, the gear comprises a driving force transmitting member engaging the engagement portion to transmit an initial driving force to the initial driving member, the driving force transmitting member being released from the engagement portion after the transmission of the initial driving force is completed.
In the gear mechanism having the above described structure, as the driving force transmitting member engages the engagement portion so as to transmit the initial driving force to the initial driving member, by changing the distance from the pinion axis to the engagement portion, the driving torque and angular velocity of the pinion to which the initial driving force is transmitted through the driving force transmitting member and the initial driving member can be changed. Thus, the driving torque and the angular velocity of the pinion can be adjusted depending on the characteristic of the rotation load to be applied to the pinion at the initial phase of the driving start. Further, be cause the driving force transmitting member is released from the engagement portion after the transmission of the initial driving force is completed, the driving force transmitting member never interfere with the initial driving member and the pinion after the transmission of the initial driving force is completed. As a result, the rotation of the pinion can be continued without being obstructed by the initial driving member.
According to a tenth aspect of the present invention, there is provided a gear mechanism according to the first ninth aspects, wherein the gear is a rack supported movably in the direction of a pitch line of the pinion.
In the gear mechanism having the above described structure, since the gear is a rack supported movably in the direction of the pitch line, when the rack is moved linearly along the pitch line, the linear movement of the rack can be converted to the rotation movement by the pinion. Thus, the pinion can be rotated by a driving force from a driving unit like a piston for generating a linear motion for the rack.
According to an eleventh aspect of the present invention, there is provided a gear mechanism comprising: a pinion; a gear meshing with the pinion; and a reinforcement member provided on the pinion for reinforcing teeth of the pinion for receiving an initial driving force from the gear.
In the gear mechanism having the above described structure, because the reinforcement member reinforces the teeth of the pinion for receiving the initial driving force from the gear, when the initial driving force from the gear is large, the teeth of the pinion can be prevented from being damaged by the initial driving force. Therefore, a sufficient rotation amount of the pinion can be secured even when the size of the pinion is reduced.
According to a twelfth aspect of the present invention, there is provided a gear mechanism comprising: a pinion; a pair of intermediate gears meshing with different teeth of the pinion, respectively; and a drive gear in which different teeth thereof are brought in mesh with the pair of the intermediate gears so as to transmit a driving force through the pair of the intermediate gears to rotate the pinion.
In the gear mechanism having the above described structure, because at the same time when the driving gear in a stop state starts to drive the pair of the intermediate gears, the driving force is distributed by the pair of the intermediate gears and transmitted to the pinion, as compared to the case in which no intermediate gears are provided, the maximum driving force to be applied to one tooth of the pinion can be reduced to substantially half. Thus, even when the initial driving force from the gear is so large that the load on the pinion becomes maximum, the teeth of the pinion can be prevented from being damaged by the initial driving force.
According to a thirteenth aspect of the present invention, there is provided a gear mechanism comprising: a pinion in which a module of a tooth is integer times the module of the other teeth and the one tooth is a beginning end tooth for receiving an initial driving force; and a drive gear in which a large tooth to mesh with the beginning end tooth of the pinion for transmitting the initial driving force and small teeth to mesh with the remaining teeth of the pinion for transmitting a driving force are provided continuously.
In the gear mechanism having the above described structure, because the module of the beginning end tooth of the pinion is integer times that of the remaining teeth, the tooth width of the beginning end tooth is larger than that of the remaining teeth in the circumferential direction. Therefore, the strength of the beginning end tooth can be largely improved than the other teeth. As a result, even when the initial driving force from the driving gear is large, the pinion can be prevented from being damaged by the initial driving force.
According to a fourteenth embodiment of the present invention, there is provided a webbing retractor for tensioning a vehicle occupant restraining webbing in a direction for restraining the vehicle occupant upon an emergent deceleration of a vehicle, comprising: a gear mechanism according to the first-thirteenth aspects; a take-up shaft to which an end portion of the webbing is fixed; a clutch mechanism linked with the take-up shaft and the pinion of the gear mechanism for transmitting a torque from the pinion to only the taking shaft; and a drive means for driving the gear of the gear mechanism upon an emergent deceleration of the vehicle to rotate the pinion in the direction for taking up the webbing.
In the webbing retractor having the above described structure, the size of the pinion in the gear mechanism can be reduced without changing the material or the like. Therefore, a winding amount of the webbing necessary for an emergent deceleration of a vehicle is secured and the size of the gear in a rack or the like meshing with the pinion can be reduced. As a result, the size of the webbing retractor can be reduced without increasing manufacturing costs and weight of the retractor.
According to a fifteenth aspect of the present invention, there is provided a webbing retractor for tensioning a vehicle occupant restraining webbing in a direction for restraining the vehicle occupant upon an emergent deceleration of a vehicle, comprising: a pinion; an internal tooth gear in which internal teeth are formed along a driving side pitch circle having a larger diameter than a driven side pitch circle of the pinion, the internal teeth being brought into engagement with the teeth of the pinion at a meshing ratio of 2 or higher; a take-up shaft to which an end portion of the webbing is fixed; a clutch mechanism linked with the take-up shaft and the pinion of the gear mechanism for transmitting a torque from the pinion to only the take-up shaft; and a drive means for rotating the pinion in the direction for taking up the webbing by moving the internal tooth gear along the driving side pitch circle upon an emergent deceleration of a vehicle.
In the webbing retractor having the above described structure, because the internal teeth of the internal tooth gear mesh with the teeth of the pinion at a meshing ratio of 2 or higher and the internal tooth gear transmits the driving force from the driving means to the pinion. Thus, as compared to a case in which the driving force is transmitted by a set of gear and pinion whose meshing ratio is from 1 to slightly larger than 1, the maximum load to be applied to one tooth of the pinion can be reduced to below half, so that the driving force which can be transmitted between the internal tooth gear and the pinion can be largely increased. Thus, the teeth of the pinion can be prevented from being damaged by the initial driving force even when the size of the pinion is reduced without changing the material or the like. As a result, the taking-up amount of the webbing necessary for an emergent deceleration of a vehicle can be secured and the size of the webbing retractor can be reduced without increasing the manufacturing cost and weight of the retractor.